Issue 54

A. Moslemi Petrudi et alii, Frattura ed Integrità Strutturale, 54 (2020) 226-248; DOI: 10.3221/IGF-ESIS.54.17

 Kinetic Energy Launcher: A projectile that has high kinetic energy due to its high speed and mass and is therefore highly efficient in creating a cavity in the target.  Impact of the projectile (cross-section) diameter: The projectile diameter is one of the important and effective parameters in penetration. Increasing projectile diameter results in an increased cross-sectional area, and this factor reduces ballistic speed in ceramics that are brittle and exhibit brittle behavior. In other words, due to the ceramic brittle, the higher the cross-sectional area, the higher the surface of the ceramic being broken at the first moment of impact, thus facilitating projectile penetration.  Mushrooming projectile shape: The flow of projectile head material after it hits the target in a radial direction and increases the projectile cross-section.  Ricochet: The projectile crosses the surface of the striker without stopping or penetrating it.  Fracture due to initial stress wave: occurs when the initial stress wave in an impacted zone exceeds the ultimate compressive strength σ uc of the material. This can occur in weak and low-density targets.  Radial fracture at the frontal side: occurs in the frontal side of the target. This is conceivable in brittle target elements whose tensile strengths are substantially lower than their corresponding compressive values, such as ceramics.  Spalling and Scabbing is a tensile material failure due to the tensile reflection of the initial compressive transient waves from the distal side (far side) of the target and is a common phenomenon under explosive loading. Failure by spalling can occur on either the front or back of a target and is characterized by the formation of petals or ejects. Scabbing has a similar appearance, but the fracture is produced by deformation and its surface is determined by local inhomogeneity and/or anisotropies that may exist in the rolling direction.  Petaling: is produced by high radial and circumferential tensile stresses after the passage of the initial wave occurring near the tip of the penetrator. This deformation is the result of bending moments created by the forward motion of the plate material being pushed ahead of the striker, and by inhomogeneity or planes of the weakness of the target. It is most frequently observed in thin plates struck by ogive or conical bullets at relatively low impact velocities or by blunt projectiles near the ballistic limit.  Fragmentation: occur when the projectile strikes at high velocities on the brittle targets like ceramics and targets made of heterogeneous materials like concrete.  Ductile failure or the ductile hole enlargement: the impact impulse overcomes the peripheral dynamic shear strength of the target material, pushing it outward and toward the impact surface to form a crater that is much larger than the projectile diameter. At the same time, the projectile pushes into the target, and there are hydrodynamic erosion and inversion of the penetrator material against the preceding face of the target.  Plugging: develops as the result of a nearly cylindrical slug of approximately the same diameter as the bullet being set in motion by the projectile. Failure occurs due to large shears produced around the moving slug. The heat generated by the shear deformation is restricted to a narrow annulus in which it decreases the material strength resulting in instability and is called an adiabatic shearing process. Plugging is most frequently found when blunt penetrators strike intermediate or thin, hard target plates. Its presence is sensitive to velocity and the angle of obliquity of pointed projectiles. Shear plugging is generally observed for thick targets, particularly with high strength materials. In these instances, an intense shear band may be observed intersecting a tensile opening at the stretched rear surface.  Discing failure: in the case of discing, shear cracks develop in the plane of the plate as a consequence of in-plane shear stresses induced by bending. Both metallurgical inclusions and inhomogeneity in the plane

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